Field of the Invention
The present invention relates to an X-ray optical axis adjustment device used with an X-ray analyzer that performs measurement by irradiating a sample with X-rays emitted by an X-ray source, and detecting X-rays released by the sample in response to the X-ray irradiation using an X-ray detector.
Description of the Related Art
The X-ray source of the X-ray analyzer is an X-ray focus constituted by a region in which electrons emitted by a cathode such as a filament collide with an anticathode. The X-ray detector is a zero-dimensional X-ray detector not possessing a function of detecting X-ray intensity according to position (i.e., X-ray intensity positional resolution), a one-dimensional X-ray detector capable of positional resolution within a linear region, a two-dimensional X-ray detector capable of positional resolution in a planar region, or the like.
A zero-dimensional X-ray detector is, for example, an X-ray detector using a proportional counter (PC), an X-ray detector using a scintillation counter (SC), or the like. A one-dimensional X-ray detector is, for example, an X-ray detector using a position-sensitive proportional counter (PSPC) or one-dimensional charge-coupled device (CCD) sensor, or an X-ray detector using a plurality of one-dimensionally arrayed photon-counting pixels, or the like. A two-dimensional X-ray detector is, for example, an X-ray detector using a two-dimensional charge-coupled device (CCD) sensor, an X-ray detector using a plurality of two-dimensionally arrayed photon-counting pixels, or the like.
When performing measurement using the X-ray analyzer described above, the centerline of the X-rays reaching the X-ray detector from the X-ray source (i.e., the optical axis of the X-rays) must be set at fixed suitable conditions. The process of setting the optical axis of the X-rays to fixed conditions is generally referred to as adjusting the optical axis.
The optical axis is adjusted by, for example, sequentially performing adjustments such as 2θ-adjustment and θ-adjustment. These various types of adjustment will be described hereafter using a fixed-sample X-ray analyzer as an example.
(I) Fixed-Sample X-Ray Analyzer
First, the fixed-sample X-ray analyzer will be described. In FIG. 15A, a fixed-sample X-ray analyzer 51 comprises an X-ray focus F constituting an X-ray source for emitting X-rays, a sample stage 52 for supporting a sample S in a fixed state, and a zero-dimensional X-ray detector 53 for detecting X-rays given off by the sample S. The X-ray focus F is an X-ray focus for a line focus extending in a direction passing through the surface of FIG. 15A (hereinafter termed the “drawing surface-penetrating direction”). The X-ray focus F may also be a point-focused X-ray focus. An incident-side slit 54 is provided between the X-ray focus F and the sample stage 52. The slit groove of the incident-side slit 54 extends in the drawing surface-penetrating direction in FIG. 15A. The sample stage 52 supports the sample S so that the sample S extends in the drawing surface-penetrating direction.
The X-ray focus F and the incident-side slit 54 are supported by an incident-side arm 55. The incident-side arm 55 rotates around a sample axis X0 extending through the surface of the sample S in the drawing surface-penetrating direction, as shown by arrow θs. This rotational movement may be referred to as θs-rotation, and an operating system for effecting such θs-rotation may be referred to as a θs-axis. θs-rotation is effected using an actuating system comprising a motor of controllable rotational speed, such as a pulse motor, as a power source.
A receiving-side slit 56 is provided between the sample stage 52 and the zero-dimensional X-ray detector 53. The slit groove of the receiving-side slit 56 extends in the drawing surface-penetrating direction in FIG. 15A. The receiving-side slit 56 and the X-ray detector 53 are supported by a receiving-side arm 57. The receiving-side arm 57 rotates around the sample axis X0 independently of the incident-side arm 55, as shown by arrow θd. This rotational movement may be referred to as θd-rotation, and an operating system for effecting such θd-rotation may be referred to as a θd-axis. θd-rotation is effected using an actuating system comprising a motor of controllable rotational speed, such as a pulse motor, as a motive power source.
When using the X-ray analyzer 51 to perform X-ray diffractional measurement upon, for example, a powder sample S, the X-ray focus F and the incident-side slit 54 are θs rotated by the incident-side arm 55 continuously or stepwise at a predetermined angular velocity, while, simultaneously, the receiving-side slit 56 and the X-ray detector 53 are θd rotated by the receiving-side arm 57 continuously or stepwise at the same angular velocity in the opposite direction, as shown in FIG. 15B.
The angle formed by a centerline R1 of X-rays incident upon the sample S from the θs-rotating X-ray focus F with respect to the surface of the sample S is represented by “θ”. In other words, the angle of incidence of the X-rays incident upon the sample S is represented by “θ”. The centerline of the X-rays is labeled R1, but, in the following description, the X-rays incident upon the sample S may be referred to as incident X-rays R1. The θs-rotation of the X-ray focus F may be referred to as “θ rotation.”
When the X-rays incident upon the sample S meets certain diffraction conditions with respect to the crystal lattice plane of the sample S, the X-rays are diffracted by the sample S (i.e., diffracted X-rays is given off by the sample S). The angle formed by the centerline R2 of the diffracted X-rays with respect to the surface of the sample S is always equal to the X-ray angle of incidence θ. Accordingly, the angle formed by the diffracted X-rays with respect to the incident X-rays R1 is twice the X-ray angle of incidence θ. The angle formed by the diffracted X-rays R2 with respect to the incident X-rays R1 is represented by “2θ”.
Meanwhile, the θd-rotation of the X-ray detector 53 is performed at the same angular velocity as the θs-rotation of the X-ray source F, with the result that diffracted X-rays R2 emitted from the sample S at angle θ are received by the zero-dimensional X-ray detector 53, which forms angle θ with respect to the surface of the sample S. The X-ray detector 53 forms angle θ with respect to the surface of the sample S, but always forms an angle equal to twice θ with respect to the incident X-rays R1. For this reason, the θd-rotation of the X-ray detector 53 may be referred to as “2θ-rotation.”
(II) 2θ-Adjustment
Next, 2θ-adjustment will be described. 2θ-adjustment refers to adjustment performed so as to correctly align the angle 2θ=0° detected by the X-ray detector 53 and the centerline of the X-rays from the X-ray source F reaching the X-ray detector 53. When performing such adjustment, the incident-side arm 55 is first set at an angular position of θs=0°, and the receiving-side arm 57 at an angular position of θd=0°, as shown in FIG. 15A. That is, the X-ray detector 53 is set at an angular position of 2θ=0°.
Next, the sample S is removed from the sample stage 52 to allow X-rays to pass freely through the position of the sample, a incident-side slit 54 of roughly 0.1 mm is set, a receiving-side slit 56 of roughly 0.15 mm is set, the X-ray detector 53 and the receiving-side slit 56 are positioned at 2θ=0°, the X-ray detector 53 and the receiving-side slit 56 are intermittently θd rotated at, for example, steps of 0.002°, and diffracted X-rays are detected by the X-ray detector 53 at each step position. A diffracted X-ray peak waveform such as that shown in FIG. 16A is thus found.
If the amount of deviation of the 2θ-angular position of the center P0 of the full width at half maximum intensity (i.e., FWHM) D0 of the peak waveform with respect to the angular position 2θ=0° of the X-ray detector 53 is within a predetermined tolerance, such as (2/1,000)°, 2θ-adjustment is considered to have been accurately performed. On the other hand, if the amount of deviation of the 2θ-angular position of the center P0 of the full width at half maximum intensity D0 with respect to the 2θ=0° of the X-ray detector 53 is outside of tolerance, the position, for example, of the receiving-side arm 57 in FIG. 15A is adjusted to adjust the position of the X-ray detector 53 and the position of the receiving-side slit 56, after which 2θ-adjustment is again performed.
2θ-adjustment can also be performed by correcting data obtained as the result of actual X-ray diffraction measurement according to the amount of deviation calculated, rather than by moving the position of the X-ray focus F or the X-ray detector 53.
(III) θ-Adjustment
Next, θ-adjustment will be described. In FIG. 15A, θ-adjustment involves adjusting so that the surface of the sample S is parallel to the X-rays R1 incident upon the sample S from the X-ray focus F. When performing such adjustment, the incident-side arm 55 is first set at an angular position of θs=0°, and the receiving-side arm 57 at an angular position of θd=0° in FIG. 15A. That is, the X-ray detector 53 is set at an angular position of 2θ=0°.
Next, an optical axis adjustment jig 58 such as that shown in FIG. 16B is attached to the sample stage 52 instead of the sample S shown in FIG. 15A. In this case, reference surfaces 59a, 59b on the two shoulders of the optical axis adjustment jig 58 facing the optical axis R0 shown in FIG. 15A. Next, the θs-axis and θd-axis are simultaneously rotatingly oscillated the same number of degrees within small angular ranges in opposite directions around the sample axis X0 near θ=0° (i.e., X-rays reaching the zero-dimensional X-ray detector 53 from the X-ray source F are kept in a straight line as the X-rays are rotatingly oscillated around the sample axis X0) to find the angular positions where X-ray detector 53 output is maximum. The angular position of the X-ray focus F and the X-ray detector 53 is then determined to be the position at which θ=0° can be attained.
Techniques for performing conventional X-rays adjustment as described above are disclosed, for example, in patent document 1 (Japanese Patent Laid-Open Publication H01-156644), patent document 2 (Japanese Patent Laid-Open Publication H01-156643), patent document 3 (Japanese Utility Model Laid-Open Publication H01-158952), patent document 4 (Japanese Patent Laid-Open Publication H03-291554), and patent document 5 (Japanese Patent Laid-Open Publication 2007-017216).
In a conventional X-ray analyzer, as described above, an optical axis adjustment jig comprising reference surfaces on two shoulders thereof is used when performing θ-adjustment, and changes in X-ray intensity magnitude are measured while the zero-dimensional X-ray detector is continuously rotated. Such a conventional analyzer apparatus presents the problem that an extremely long time is required to perform measurement.